1. Field of the Invention
The present invention relates in general to flexible plastic tubing and, more particularly, to apparatus and methods for making such tubing, which tubing is flexible and includes an external helical support rib or bead. More particularly, this invention relates to such a tubing product having a main elongate passage or lumen in which fluid may flow, and which may also include one or more additional lumens defined or carried within the support bead, as well as one or more electrical conductors which may be used, for example, to effect electrical resistance heating of the fluid conveyed in the main lumen, or which may be used to convey electrical signals along the length of the tubing. The tubing product may also include one or more optical fibers, which also may be used, for example, to convey optical signals along the length of the tubing or to convey light which may be used for illumination or to power a photovoltaic device.
2. Related Technology
Tubing which is flexible, and has a relatively thin wall and an integral helical supporting bead is known in the art. Such a flexible support-bead tubing construction provides substantial crash resistance while leaving the tube wall flexible enough to permit short-radius bends without collapsing or kinking the tube. The versatility of this kind of tubing is evidenced by its wide applicability in construction, ventilation, manufacturing processes, auto washes, medical devices, hospitals and other fields.
The walls of a support-bead tubing can be quite thin to minimize overall weight. This light weight for the tubing is an important feature when, for example, the tubing is used with an inhalation machine to provide a patient with more comfort during oxygen or medicated air delivery. Two other features of known thin wall support-bead or bead-reinforced tubing are transparency and smoothness of bore. Transparent plastic material permits inspection of the fluid coursing through the tube, to detect, for example, the presence of moisture in an anesthetic or patient oxygen delivery application. A smooth inner surface of such a tube is desirable to keep the tube free from deposits of contaminants and to discourage non-laminar flow. Also, this smooth inner surface makes the tubing product more desirable for applications in which the tubing is to be re-used. The smooth inner surface promotes easy and effective cleaning, sanitizing, and sterilizing of the tubing product.
U.S. Pat. No. 3,910,808 to Steward, discloses apparatus for forming a thin-walled, flexible, crush resistant tubing having a support-bead. Steward discloses a method for extruding a plastic strip having a longitudinal rib, and the method and apparatus for helically winding the strip about an axis to produce a corrugated flexible tubing having a smooth bore and a helical external support bead.
Many applications, however, require or are enhanced by the presence of controlled heating of such tubing. Neonatal patients, for example, as well as patients in shock or who are sustained on breathing equipment, are among those who benefit from gas flowing through heat-conditioned tubing.
U.S. Pat. No. 5,454,061 to Lenart Carlson, provides a helically wound and helically ribbed plastic tubing incorporating an electrically conductive heating wire and an apparatus and method for making the tubing. In this patent a plastic ribbon is wound about an axis into a tube with one edge of each lap overlapping and heat bonded to an edge of the preceding lap as the tubing is rotationally formed. A conductive wire is embedded in the ribbon and a bead is applied and heat-bonded onto the tubing, encapsulating the conductive wire during rotation of the tubing, and providing a unitary structure including a conductive wire integral to a flexible tubing. Again, the tubing has a corrugated crevice-free outside surface and a smooth inside surface. Coolant is applied to the tubing for cooling the unitary ribbon, wire, and bead during formation of the tubing, and also to assist in advancing the tubing along the axis of the manufacturing apparatus.
One prior application of a hollow ribbed pipe can be found in U.S. Pat. No. 5,051,081 assigned to Toyox. In this patent hollow ribs are produced by extrusion, and are then wrapped around the outer periphery of an extruded pipe. This construction of a tubing product has several deficiencies. For example, the interior walls of the hollow rib produced by this apparatus contain connection lines through which a gaseous material could escape into the ambient, and the rib is extruded in such fashion that it would not be possible to separate it from the tube and attach it to a hose barb. That is, the shape of the lumen or passage in this rib is not generally round.